So what is the diff between the normal speer primers and the Bench rest ones?

Price.

Benchrest or match primers are made with cups and anvils made in new dies.

One of my benchrest shooter friends toured the plant where CCI makes their BR primers. He said those primers are made on the same machine, while all other primers are made on a variety of machines, then packaged together.
Several years ago, I did some in-formal testing on the differences between standard and BR primers. The test rifles were a model 70 Fetherweight in 6.5x55, a 700 Mountain Rifle in .257 Roberts and a 700 PSS in .223. In the first two I used CCI standard, CCI BR, Fed standard and Fed Match. In the .223 I used CCI Br, Fed Match and Rem. BR.
I don't recall the exact group size with the first two rifles (roughly 3/4"), but I got best results with CCI BR, followed closely by Fed. Match. The difference was about four tenths of an inch at 100 yards for five shot groups. The Fed Match shot groups that were roughly 1/2 smaller than standard primers. I could not detect much (if any) differnce between the variuos brands of standard primers.
The results for the .223 were roughly the same, only Rem. BR's turned in the best group (.288 for 5 shots @ 100y). All three rifles were bedded and had trigger jobs. The .223 had the lugs lapped.
My conclusion was BR primers are probably worth while in target grade rifles, but probably not so in hunting rifles. They cost a little more, but I still use BR primers in all my scoped rifles, unless accuracy dictates otherwise. The only time I've found that BRs didn't help accuracy was with my Hornet, which prefers WSRS. Hope this shed some light.

Good on ya Mike thanks for that mate, very helpful. I do seem to be turning in slightly better groups with the BR's yet have'nt done a lot of experimenting. You have saved me the time, they dont seem too wildly more expensive...am using a 700P, .223, would be interested in the best load you made up for it.