By the sounds of what people were saying about them on here a while back and from experience of the old ones If you want it for bike use try to get an older one off ebay.co.uk, it sounded like they went "fashion" a few years back and are using lighter leather.
If you can get an old one it should have many years left in it and after twenty years or so they should just about be broken in by now and if you are going to have a little "off bike incident"they do take the tarmac on very well.
I'd heartily recommend Lewis Leathers. I've got a new Super Monza and it's a fantastic jacket, very well made and beautifully tailored. The leather is about 3oz I'd say, and is extremely supple and water resistant (kept me nice and dry on my motorbike), it has a very fine grain and the owner of LL told me that they use the 'closest to flawless hides' that they can. When I visited the shop/HQ I really got the impression that it's a labour of love, they have a large collection of old jackets on display and are very knowledgeable about the old British M/C jacket companies.
I own a couple of Aeros and have had a few others in the past, and it's true that the Lewis isn't as heavy and the leather is thinner, but that's not a bad thing in my book, it certainly makes the jacket a lot more comfortable.
. As for the price, yes, 600quids is a bit expensive, but after the price increase, I honestly don't think Aero is that economical anymore.