Not sure where you got those numbers either. You weren't looking at velocity of propagation numbers, where you?
Anyway, at 144MHz, here it is:
25 feet of Belden 9258 RG-8x = 1.013 db of loss
18 feet of Belden 8240 RG-58 = 0.604 db of loss
Figure .4 db in connector losses for the joint where the two meet, and you are looking at 2.017db of loss. The .4db number may be slightly off, but it isn't going to change much.
If your entire cable run is the 43 feet, then 2db of loss isn't too bad. You can certainly do better, but no matter how much you spend, you'll always be able to do a bit better. Use a dual band antenna with some gain, and you'll overcome the feed line loss. Losses are going to be worse on the UHF side, totaling 3.588. Consider that loosing 3db is loosing half your signal. Again, a gain antenna will overcome some of this. If at all possible, I'd stick with at least one cable type to eliminate the small connector loss, or try and go with a larger/lower loss cable all the way through.