Firewall Suitability 60F or 100F

I am new to FortiGate and usually use SonicWALL's we need a new firewall and looking at a HA cluster with 2 FortiGate's the SonicWall cost pushes them out of the ball park for us and looking into FortiGate's

We have a leased line on a 1GB bearer but currently using 100mbps up & down.

I have 2 external companies advising 2 very different firewalls.

Company 1 is: FortiGate 100F with UTM Protection

Company 2 is: FortiGate 60F with UTM Protection

We plan to use DPI SSL and the full UTM Suite to maximise protection but I am unsure about the 60F as we are on the verge of the staff numbers that FortiGate advise of. The SSL inspection throughput is 630Mbps  and the 100F is 1 Gbps  one thing I don't want to be doing is having to buy 2. I think the 100F is better for us and gives us scope for growth and possible upgrades where the 60F puts us in a limited area. I have looked at the data sheets but wanting to get experienced FortiGate's users viewpoints and opinions on the matter. 

Thanks in advance.