Auto-negotiation question

Hi,

I have a 1 gigabit LAN backbone comprised of CAT6 cabling throughout and Netgear GSM7248 switches. A 128Kb/s IP-VPN line was installed on our network recently to access a system that HQ is rolling out group-wide. The gateway for the IP-VPN line is a Cisco router with a 100Mb/s interface connected to a port on our 1Gb/s switch which is configured to auto-negotiate speed (default).

It has been reported that the response time when accessing this new system from our site is slower than experienced at other sites; ironically the one with the fastest backbone. Someone has suggested that because the other sites all have 100Mb/s backbones, the same speed as the IP-VPN router's interface, there is no need for speed negotiation and therefore no delay in routing packets. Is this for real?? Would this cause a noticeable delay? If so, would configuring the port to which the Cisco router is connected to 100Mb/s (non-negotiable) fix this problem. I know you might say, "why don't you just try it?", but the line is kind of already in production and I didn't want to go messing around with it unless I was reassured that it would have a strong chance at fixing the problem.

TIA.

TIUK-3000