There are way TOO many theoretical discussions about speed of timeline play versus card specifications here and everywhere.

Here is what gives in the real world - If you are using a recent version of VegasPro like Version 13 build 373 - there are several important factors here in the real world. AND the Largest factor - what you have on the timeline and how you are previewing the timeline. Lets say you have a straight forward codec for video playing back at normal speed in a preview set to BEST project property render/preview - then just add a simple alpha mask to this timeline by placing it on a higher level track to composite this image. YOU can SLOW down your project to a crawl with just this one step - just imagine what you could do with adding mutliple effects all at the sametime.

Forget the video card non-sense and concentrate on what you are trying to achieve with a workflow and an outcome that is desirable.

i think you might be over-complicating the issue...

what i, and i'm sure many others, are looking for in playback is on a much more basic level.

a. given raw footage, say, avch, 4k, etc., which card will give consistent preview / full playback at original frame rate WITHOUT anf fx. (i'm not bring cpu into consideration, working on the principle most serious editors will have a min i7)

b. which card can handle your given example, ie. raw + alpha mask, to achieve the best frame rate.

i am perfectly aware that loading fx etc., will slow down even the best of cards, but what i'm looking for is simple reliable playback using gpu, which scs seems to have given up giving specs on.

so far, from what i've read, r9 280/290 appears the best, but i'm loathed to go the amd route and as yet, no one seems to be attempting to answer what's happening with cards AFTER the 580 for nvidia.

@Steve
Thanks for that link, the gtx 970 looks promising at a reasonable price, but again its guess work as to to how it will benefit the timeline performance.

@VideoIT
Im not sure what point you are making. I do add effects and always will, my media matches the project properties and as we all know, it slows to a crawl. This is what I want to improve with the benefit of the experience of forum users. Whatever means achieves this is what I want. The wisdom seems to suggest a better gpu will help and so I'm persuing that course.

@Ushere
I've come to the 290 conclusion myself but without any hard evidence. The GTX 970 seems very powerful at the price and has more cuda cores than 470 but I don't know if that aids the timeline. ; )

Derm

@Derm

If CUDA cores is all it takes for Vegas, the 600 and 700 series cards all have more cores then a GTX580 and yet are not any better but rather worse. As of today, the FERMI based cards are the best Nvidia has to offer for Vegas; I can't speak for the 900 series.
If you currently have a GTX470 the upgrade to a R9 290 or GTX580 will improve your performance by 100%. Put two in it and you get another boost but that is more for rendering and multi monitor environment.
People that don't like GPU acceleration are those that can't get it to work. Search for a user by the name BruceUSA, he's got one or even two R9 290 in his system and he swears by it.
However, keep in mind you need a good and branded power supply to get it working properly. If you look at my system spec you will see what is in my editing machine. This system can handle 1080i, 1080 30p with all kinds of effects, as long as we are talking about Vegas own library, and preview at Best/Full. 1080 60p only works well at Best/Half or Good/Full. 4K is only possible with proxies. If you want more like 4K and beyond, you are looking at a dual Xeon setup together with the above mentioned GPUs. If money is not an issue, drop in a AMD FirePro 9000 series card and you should be good to go.

A good test of your systems playback and render performance is still Sony's own benchmark project. Us it to see how for system can take. I keep on system for testing of new settings and hardware and also for testing my system after a windows update.

Thanks Smoke, some useful information there. It was Bruce's posts that alerted me to the 290. Second hand 580's are available at a reasonable price here but I would need a greater power supply for the dual set up, as you pointed out.
Something else I have learned in this process is the topic of Script Mining, when buying a used card. I knew nothing about this. Apparently there are a lot of second hand cards on the market that have been used 24/7 for Script Mining and so are pretty worn out. This has put me off the idea of buying a used card as you cant always rely on the honesty of the seller.

I thought that AMD's are more used for mining rather then Nvidia.