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Hi Paul,
I am very happy with my 13E. In fact, it is my favourite EP. It is very easy in terms of eye placement, has comfortable eye relief (I do not wear glasses when observing), and does not really need a Paracorr - its correction is excellent.
At a focal length of 2513mm, I get a magnification of 193x which is fantastic for galaxy hunting and fine galaxies on steady nights. However, at such a relatively high power, there are some nights when I cannot use it because the seeing cannot sustain that power.
At your focal length, a 13E would give you 115x magnification, which would make it for you a nice low-mid power EP with roughly 52 arc minutes FOV. This would be wonderful for open cluster and nebulae.
A 10E would be better if you want to hunt down galaxies and fine globulars at 150x. An 8E would be pushing things a bit, at about 187x, and you may not get quite as much use out of it.
Some like me love the immersive FOV of the ethos, others feel a little overwhelmed by it. The best advice would be to go to an observing night and try in your lightbridge to see how the various iterations suit your set-up.
The degradation to your mirror may not be as bad in terms of actual use, even if it looks bad in the light of day. The human eye has trouble detecting anything less than a 10 per cent difference in brightness, so let's say you have lost about 8 percent of the light through the damage, what you are looking at is probably almost identical to what it would look like with a pristine mirror.
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