The slimline coil is very susceptible to instability. I had one of the later slimlines, the one that's not supposed to have any problems, but it was still problematic. When my buddy bought his SE, his slimline was the same as mine. When I was a newbie just starting out, I really didn't know anything was wrong with the coil, until after using it for a few months, and then buying some other aftermarket coils, including an Explorer 1050 coil. I was finding silver with the slimline, no doubt, but when I decided to try an older 1050 coil (a friend suggested I do), the increase in performance was very recognizable. More stability in all ground conditions, and it hit harder on deeper (7"+) targets. I remember comparing some really deep signals with my buddy who was still using the slimline. Suffice to say he had a 1050 coil within a week after that hunt. I wish ML would have just admitted they had a problem with this coil, and to ask to have them all recalled. That would have been a moral decision for the company.
Truthfully, between those two coils you mentioned, I'd use the 1000 coil. Better yet, get a new Pro Coil, and you'll never have to worry about asking questions like this again.
HH,
CAPTN SE
Dan