Shudder problem - my arse! to tell you the truth, if there was a major problem with a Shimano reel then they would have called them all back, that’s how they work. Also if there was a shudder problem, then many of us on here would have heard about it, not just a couple of rumours. I have no association to Shimano whatsoever, just know I haven't had any issues with mine. I tend to send mine in for service once a year which costs me ?21 all in including P&P for three and they come back to me within the week.
Fact - they are the most popular carp reel around, thousands can't be wrong.
However, reels are like rods, in that it’s all about personal taste. Once I switched over to the Baitrunner system, I never looked back. I have caught many fish on mine and I'm 100% confident. With regard to what reel to choose from between the 8000 and the 10000 then may I suggest you consider your venue options. If you know categorically that you will be fishing small venues lets say up to 10 acres then go with the 8000's and save a few quid, but if you feel that you may occasionally fish the larger venues or there might be the possibility of doing a French trip etc, for the extra 15 quid or so, you might as well go for the 10000's. To recap, Shimano baitrunners are superb mate and I strongly recommend them. As I said earlier, I looked at the big pit reels and opted for the 8000's and 10000' due to the extra built in feature of being able to click over the bait runner and sleep easy until the buzzers go berserk and you pull into that PB. Rather that, than worry mate!