Just go on price,
There will be no noticable differance in performance, 1 or 2 FPS is all. The HIS card in my experiance will be the better quality card and as you said its an Ice Q version it will come with the cooler that exhausts the hot air out of the back of the case which i prefer over the standard fan which simply circulates air within the case.
It really is too close to call on performance but teh GDDR 4 will be that little bit faster, as i said not a lot but a little.
Yes it will be fine it takes all its power from the motherboard so doesn't need extra power cables.
I have looked at some reviews regarding this, Standard GDDR3 4670 Vs GDDR4 4670 and the HIS 4670 Vs a standard GDDR3 4670 and both the GDDR4 Sapphire card and the HIS card come out on average 2% faster than the standard GDDR3 card.
3% @1024 x 768 and downwards from that.
So based on that the cards will be very close together performance wise, I'm guessing based what i know that you may get slightly better minimum FPS with the GDDR4.
As far as support goes then you can really only go on experience, ct1615 says HIS are bad, I have owned 3 HIS cards and never needed them. Others i have seen say Sapphire are bad, again never needed them so i couldn't begin to guess which would be best from that stand point.
If you are just wanting to plug it in and forget about it then the GDDR 4 is probably where you should go. Personally i like the HIS card for the reasons i mentioned above which means it has a better chance of overclocking to a better/ higher degree.
At the end of the day you wouldn't be doing much wrong in my book if you just went with a gut feeling or got the one you liked the look of best, it really is that close.
One thing that does spring to mind now i posted, which is typical
The HIS card uses a cooler that will take up two slots or to put it another way the card will ge twice as wide as a standard Sapphire one so that may make your choice for you. Take a look and see.
ct1615 says HIS are bad, I have owned 3 HIS cards and never needed them. Others i have seen say Sapphire are bad,
I have never owned a HIS, although I have owned Asus, Gigabyte, MSI, XFX, and EVGA. If you search through this forum though you will read several horror stories about HIS tech support, more then any other manufacturer. Hence why I would pick Sapphire over HIS any day but that is my personal feelings about HIS.
It is a marketing gimmick. Many mid to low end cards have way more memory than they can actually use....and everyday people who do not know any better see them and think...."Wow more must be better right?" never knowing they are being had. Sometimes these cards actually perform worse than the cards with less.