Bandwidth allowance goals

On a Balance 210 on the Mobile Internet WAN, I know you can set your monthly allowance and have it disconnect at 100% usage etc etc.

I am allowed 5gb/mo on my mobile internet plan without getting into overage charges.

Is the only way to control the rate I reach the maximum (so I finish my billing period at ~4.5-4.75gb) to set weighted balance on outbound policy after approximating the rate of bandwidth consumption and balancing it against my unlimited DSL lines?

Assuming no other special outbound policy, if the site uses a total of 35 gb/mo, I should set weighted balance to 3:3:1? 15 gb each on unlimited DSL and 5 gb on HSPA stick? 4:4:1 for just a little more buffer? Does the 210 throttle automatically to arrive at my maximum making policy like this redundant?

Your weighted balance approach is correct. I would start at 4:4:1 first and monitor it closely for a couple months. The Balance will not throttle the speed of the WAN connection, it will let it go full blast. So, if the 1 session that happens to go across the Mobile WAN is a large file download or HD movie it could easily chew up your 5GB.

But if you have it set up to shut down at 100% usage then the traffic will be balanced equally across the two DSL lines until the next billing cycle starts.