Try a three. You really want to be safe dial it down to 2. I just used the slim for two weeks and for the most part any setting on or below 3 is considered safe.
I've got both, and have been keeping the Slim on 5 for awhile. Same easy, close shave with either. I could live with either as an only too.
95% of the differences between shaves is hydration and technique IMO. We talk about tools a lot but after you've got a reasonably decent razor and soap tools don't affect the shave all that much.