Jweb & PDF (again)

So, now that pdf's no longer crash jweb (hooray!), I'm looking again at an app I've been working on for which this is quite a crucial issue, and I have a question about performance.
On my mid 2012 15" MacBook I can load a PDF into jweb and it loads almost instantly, and the scrolling etc. performs well.
However, in my 2010 Mac Pro, it can sometimes take over a minute to load even a small pdf, and scrolling is abysmal, happening several seconds after the gesture.
And I mean sometimes; performance weirdly seems to vary from day to day - sometimes pdf's won't even load at all.
I realise that this Mac Pro is an old machine, but I'm just wondering what performance is like on a 'average' machine (if there is such a thing!), and what spec (presumably something relating to graphics card?) would be required to expect usable performance.

Also, is there a way to turn a pdf page programmatically yet, ideally with a keystroke or controller message?
TIA