Does anyone have any real world experience with performance gain
from going from one to the other? We have noticed a lot of issues with
the Black Diamond's performance. The support staff tells us we should
QoS everything down to the last packet, but we don't really feel that we
should have to considering the amount of money we spent on this device.
Perhaps I'm asking too much, who know. Some issues we have are: Even
though the CPU shows 97% idle it from one server to the next connected
to the same switch its 40ms between them. "Spikes" of
inexplicable/random lag that only seems to effect VoIP/Game Server type
applications. We're just trying to find opinions to see if A) anyone is
using these switches successfully, B) if anyone had problems with them
and switched, or C) if anyone has ever heard of a switch that even
though its 97% idle it still has performance issues 
Off-list is fine, and I'm not trying to bash Extreme Networks.
Thanks,
-Drew
Unless you have brand spanking new linecards and the MSM3, all ICMP packets will be CPU routed on the BD (and all Extreme Networks i-chipset platforms).
We successfully use BD6808 with ICMP hardware routing blades and MSMs, plus the ip-subnet-lookup feature in EW7.3 which brings it up from a "route-cache is a /32 type platform" into giving it an additional network size (we use /16) route-cache with 128k entries. These changes enables it to being able to route todays internet.
If the CPU is 97% idle I don't really see that you should have this problem, the above two solves the issue where netTask (which handles forwarding tables being programmed into ASIC plus CPU forwarding of packets) is very high, which is not your case.
If you don't use it as a router, none of the above applies to you, the BD6800 is an excellent L2 switch that should never have any problems what so ever unless you flood it with multicast (a la slammer).
How do you measure the latency, that you say is 40ms? If you can measure it with anything else than ICMP then you might see other results.
I am behind several right now and we're running voip and gaming over them.
About changing, if you're planning to move to 6500 with Sup720-3B(XL) then you'll get a very capable platform, which is at least one generation newer in performance etc. The BD6800 wwith i-chipset blades was released in 1999. Personally, I like both of them, they're good at different things.