In this thread over at cisco-nsp mailing-list, there was a talk about using 3560 with financial flows that you could find useful.
It doesn't answer your question about latency, but explains why using this switch with financial flows is not such a good idea.
With bursty traffic like financial data, you'll probably see output drops, meaning that the output buffers of the switch are too small. You could set up some CoS, but CoS is only the way to tell the switch which packet to drop, but that is not a solution with critical data that has to be delivered and not dropped.
I'd like also to quote Joshua's answer:
The buffer sizes on the small form-factor cisco switches are too small
for anything but a quiet office lan. The exception is the 4948.
As others have mentioned, you can play with mls qos/buffer tuning,
but, i personally would recommend planning an upgrade to something
that is more capable.
There is also two cisco papers regarding switch performances, but they don't talk about latency:
Cisco switching performance product sheet.
Cisco Switch Guide.
And the router equivalent.