Intel 2915ABG on 5ghz wifi, how good/bad can it be

[kfzhu1229]

Anyone is trying to use 5ghz 802.11ac wifi on a 2915ABG card from a T4x/R5x?
I have a lot of friends who don't know the difference of 2.4ghz and 5ghz and/or their devices are new enough to operate on 5ghz 802.11ac, so I've had a lot of trouble with my 2200bg card. Neither does my newer T530 work with 5ghz wifi. I have tried 2915abg card on 5ghz and it works as fine as 802.11ac cards in terms of actual functionality. I've heard people saying that the 2915ABG card isn't all that great or something, but speedtest.net does show improvement over 2200bg because of the 5ghz frequency.
My question here is how good/bad can it be for a 2915ABG card to use the 5ghz band?