I believe that there is no need to use TEMAC for 10/100M Ethernet
port on Spartan3E Starter Kit.
What I think of the difference between TeMAC and EthernetLite is
that the former is not free, but can support 1000M Ethernet,
however the latter one is free, supports only 10/100M Ethernet.
Moreover, TeMAC has DMA functionality for boards who has SDRAM
available using MPMC.
Considering the performance, I think you should verify the cause.
According to my experience, the bottleneck of the overall internet
performance lies at the tcp/ip stack running on microblaze together
with xilkernel. So, switching from ethernetlite to TeMAC will have
no improvement on performance. If you want to reach full bandwidth,
probably, you need a hardware based tcp/ip stack. Otherwise, the
data transmission speed will be about 2MBytes per second at most.