Best graphics card for Second Life?

Im trying to decide on the best video/graphics card for my new system upgrade, for use on Second Life and Adobe CS5 in April.

System Specs:
Lenovo K210 Idea Center
Intel Core Quad 2.4GHZ Q6600 (may overclock if neccssary, any opinions?)
stock mobo
4GB DDR3 RAM
1 PCIe x8 Slot (replacing stock GeForce9300ge)
(planned upgrade PSU)OCZ Fatal1ty OCZ550FTY 550W ATX12V@25A 80+ SLI Ready CrossFire Ready ($44@newegg)
Blu-Ray optical drive
21.5" HD Monitor (plan on using highest resolution possible)
Windows 7 ultimate -64bit

Planning to spend $100-150 on a new graphics card. I am mainly concerned with bang for my buck and making the right choice for my system and needs, as opposed to overspending... The word is, ATI cards have problems with Second Life, which runs on OpenGL, so I am leaning towards Nvidia. Not sure if this is based soley on the use of OpenGL or what, but one of my questions is: Is comparing a graphics card's versions of OpenGL (such as 3.2 to 2.1) a viable factor when making a decision based upon Second Life performance or is this something that can simply be uptaded by new drivers?

I am looking at the EVGA GTS250 1GB DDR3 256bit OpenGL 3.0 ($140)
or XFX GT240 1GB DDR5 128bit OpenGL 3.2 ($120)

I am certainly open to any other suggestions.. I assumed I will need the 1GB as opposed to 512mb, based upon my screen size and resolution, is this correct?

Also, Will the PCIe x8 bottleneck these cards/my system noticeably? Again, mainly for Second Life.

I would greatly appreciate answers to any or all of these questions, as well as any unforseen problems you may see or suggestions you may have. Thanks