I think you have been mislead on speeds.
This is well worth a read;
Iridium Bandwidth and Internet Download Speeds/ Support | MailASail
its factual, well written and dispels many of the myths about iridium phones. Unfortunately information of this sort is difficult to come by.
I have recently installed an Iridium Pilot which is an open port Iridium link (but not in an aircraft). The speeds are reasonable and Meteox for example refreshes very quickly, web browsing is possible but akin to the old days of dial up modems. Iridium and Inmarsat supply the only products that provide a service even closely comparable with the data speeds we have been accustom to with land based services.
As PeterH says with some data compression software and given that the Meteox package is pretty small I would have thought the refresh rate would be acceptable, but I will be very interested to hear.
This is a useful emulator before you spend your money.
Sloppy - the slow proxy for dial-up modem speed simulation (slow down)
it will give you a good idea of the refresh speeds you can expect.
For tactical weather avoidance it would make sense to have already downloaded the base maps and just overlay the data.
Some like this I find useful;
Meteox.com Google Maps