We also have Tooway (our provider is SkyDSL). At SkyDSL (and especially our product) there is a traffic-shaping machanism implemented that drops bandwith after a few MB to 200kb/sek. (Technically the traffic is counted by destination IP and there is a Burst for the first 20 MB)
Making multiple TCP-connections do not circumvent this mechanism.
So my Answer will be: YES - use a Proxy.
The worst case is a Service on your pfsense box that does not gain speed.
At best case you can save much bandwidth on static content. Websites you (and your guests) visit often will gain a performance boost since cached content is served with very low (lan) latency.
Our Byte-hit rate is between 7 and 30%. The average speed increase (HIT [kB/sec] / DIRECT [kB/sec]) is between 4 and 27 percent. 12% for the last month.