My manuals show about 100 fps edge for the 6MM. I don't know if anyone makes a left hand model any more but I had one many years ago. Remington made the 788 in LH. I also had a LH 308 in the 788. I have had three each of the 6mm Rem and 243's. The first 6MM I had had the wrong twist and would only handle the round nose when it came to 100 grain bullets. Remington changed it but to late to compete with the 243 which would handle the longer bullets from the start. It hard to tell how the race would have gone had they both had the one in ten twist from the start.

in factory loads you wont see any difference, but there are two things you need to really get the most out of the 6mm. you need to handload, and the 6mm can utilize a 26 inch barrel to get more than the listed velocity (100fps) difference. the 243 wont gain as much as the 6mm w/ the 26 inch barrel. I have had several of each and really preferr the 6mm over the 243 , I still have several 6mm's, but haven't kept a single 243. If your lefty try the ruger #1's.

Now there's a bit of useless advice from a well meaning right hander. Mike, the Ruger is as right handed as they get. Try to get a cartridge into the chamber under a low mounted scope, under stress, with your left hand.

Carryin' a rifle with a 26" barrel is only useful in certain circumstances, not huntin' in heavy timeber.

The 788 was a neat rifle with a very stiff action and a fast lock time, but with the locking lugs on the rear of the bolt you couldn't load full loads. The bolt compressed and you had to use a small base die to get the brass to go back into the chamber. That reduced case life signirficantly.

Remington did make some lefthanded 700s but not very many, and evidently no one is willing to part with them while alive. If you'd like one haunt estate sales.

If you really want a left handed 6mm, buy a Savage with a worn barrel and put a 6mm barrel on it. The old style short action, called "J" by most owners would be fine, or one of the long actions with a short magazine.