Those sizes for a 900 are what everyone is using now, no worries. Flip will tell you that they handle better with a 170 on the back, but the choice in that size is very limited.
Since I know that you understand the date codes, I'll let you into a secret.
There are some proper bargains out there, being sold as old stock. In fact some of those are actually brand new stock, but the sellers say they are old to disguise an offer below the retail price, from the tyre manufacturers.
here's one example,
http://www.tyretectrading.co.uk/pire...pair-deal.html .. There are plenty more on ebay.
Just check the date codes with the seller before ordering to make sure they are not so old that they will be out of date before being worn out. Recommended tyre life is 5 years from date code.
Factor in the fitting and balancing cost, which is about £12 per wheel, some fitters are reluctant to fit tyres that they haven't sold!
I like Pirellis myself and can recommend the Diablo Strada as a nice handling good all weather tyre with a long life (6000 miles from my last rear, 8000 on the front)
I have Angel ST now and they handle very nicely although I think the Stradas were a little sweeter when new?
The performance figures for the ST are nearly identical to the Michelin PR3 in the wet and dry.
You have dual compound on the ST so they should resist squaring longer than the Strada.
Then you have the Angel GT which I have no experience of but is also an all weather tyre, with a stiffer sidewall option for heavier bikes and a spec that slightly exceeds the PR4 in the wet and dry... Not so many bargains on those yet as it is the most recent model.