TBH I would stay away from an LSD first, unless you plan on doing lots of trackdays in the near future, yes you will notice a difference, but on our average roads, I think you would get more bang for your buck with a decent fast road set up. I have managed to do without an LSD and though I wanted one my trusted compadre talked me out of it as I have not even reached the limits of the cars handling as it stands now. I think I would need to push the car very hard on a track going quite quick to feel an LSD is justified, especially when you are looking at the best part of £7-800 supplied and fitted. You can make that go quite far.
I used to argue with Nick at first but I realized I was wanting to fit an LSD at the time as that is what others were doing, and I was doing it instead of focusing on my own driving first,so I would be better able to appreciate a diff when I got one.
Sorry if that sounded preachy
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For myself I really noticed the difference new tires made (first Toyos now Yokos). Then lowering on springs and fast road set up. The next big difference to me was swapping to 16" rims. After rolling on 18's for ages I really appreciate the extra feel I get from the smaller rim and slightly thicker tyre sidewall.
Oh and I hate to say it but a nice fruity exhaust made me smile no end, ok not a lot of power difference, but I like the sound, even if I feel like a 41 year old kid at times