I think your going to find barrel life about the same in both, 300RUM & 7MM STW. Yes you have a larger bullet selections, but the BC's on the 7MM bullets are better. Your powder use is going to be about the same. Most people are going to want a muzzle brake
on a 300RUM, I had one on my sendero but had it cut off. I don't think a muzzle brake is as important on the STW is it is on the RUM. I you look around on gunbroker you might find an older sendero in the STW caliber and it should be the first version of the sendero and you won't have the big palm swell as the newer sendero, I think more people dislike the palm swell then like it.
As far as BC's go, look at JLK bullets, their 168gr 7MM bullet has a BC of 690, the 189gr 7MM bullet has a BC of 735. Then compare that to berger 168gr -BC 617 and 180gr -BC 659
With 30cal bullets a 210 berger has a BC of 631 and JLK bullets 210 bullets have BC's of 665 & 680.
If I could sell my sendero tomorrow and have enough money to buy a STW I would do it in a heart beat. Also retumbo is one of the better powders. Now on the regular 7MM I use to use IMR 4831 @ 67gr with a 162 hornady BTSP, it was very acurate and deadly on Oregon coast blacktail deer.
Good luck on your search.