First of all, I'd say you should just decide now to use an online vendor instead of a local store. Your $2K will go farther that way because the prices are cheaper and you'll be saving a couple hundred in sales tax. Also, you could probably go down to an SI2 and still stay eye-clean since your stone will be less than a carat, doing this will afford you more size. Lastly, don't buy a stone just because it might be a higher carat weight than something else. An excellent well cut diamond will look bigger than an average cut larger one. also, pay attention to the diameters of the stones, that's a much better marker of how big it is.
Since you mentioned you want to upgrade eventually, i think it's important to go through a store that will give you a 100% upgrade when you're ready.
I don't believe diamondsatcost has this sort of policy, but you can check.
Three places I recommend, I suggest you contact all of them and tell them you're looking for a white, eye-clean diamond with an extraordinary cut and you only have 2K to buy both the diamond and the setting with, they will help you out:
*Jan at Diamond Brokers Of Florida (321) 984-0757
http://www.diamondbrokersoffl.com
"...Diamond Brokers is one of the few companies that offers 100% credit for an upgrade if you would like a larger or higher quality diamond"
*Greg at Ringdesigner.com 503-670-7218
http://www.ringdesigner.com/Pages/Upgrade_Program.htm
*Jonathan at
Good Old Gold 516-798-5151
www.goodoldgold.com
"Lifetime trade in for full amount of purchase price.
Yep, you heard right. If you or your lady (without letting you know

are entertaining the thought of a bigger or higher quality diamond sometime down the road (like in case you hit lotto or somethin

I'll give you back exactly what you paid for the diamond you purchased from us and apply it towards another. Guys, this is beneficial for you in a few ways. IF your engagement breaks off, and you think you may get engaged sometime down the road, you'll already have a ring to give her, but if you don't want to give her the same ring you gave the last girl, TRADE IT IN, you're not gonna lose money on the stone. Chances are this probably won't happen to you but it's a nice security buffer"
I found this AMAZING stone with a quick look. Really, it's just gorgous. Do not let the 'I' color deter you, I bet it looks like a G or better because of all the light return. Very serious sparkle, look at the brilliancescope analysis. If it were me, I'd probably snatch this one up right away. But that's because I'm a sucker for sparkle.
0.60 I SI1 AGS000 H&A $1685 5.49-5.51x3.35mm
http://www.
goodoldgold.com/_60ct_i_si1_h&a.htm
Good old Gold is a real store in long island,NY, but Jonathan does business all over the country through the internet. He has many more diamonds than what is on his website. Give him a call.
Also, Diamond Brokers of florida is also a real store in Melbourne, Fl. It's nice to know you're working with somebody that's been in business for a while, especially since you want them to be around long enough for you to get your upgrade!
Good luck and keep us posted!