I guess 1.90 for cash was a little while ago when the xrate was just under 2.00.
About three weeks ago I purchased $1000 at 1.830 from Barclays. I know it went slightly higher afterwards, and a friend has just returned and told me his average rate as per credit card purchases was 1.84.
The mid-rate is currently between 1.8750 and 1.88, so the tourist/cash rate will be i.r.o. 1.80.
Historically anything above 1.80 is in my opinion good when I compare to times when it has been below 1.50. That hurt.
I have to say that I would be tempted to buy some now. If it goes higher, well it's still a good rate. If the dollar strengthens/pound weakens for various global economic reasons you'll wish....
Never attempt to sell at the top or buy at the bottom!