Hey Tanner, to answer your question...
1. "I am wondering when and if cambium will be coming out with a 500mbps 802.11ac sm."
First off, Sakid, the ePMP Product manager, has mentioned in this forum that they're working on developing an 802.11ac platform. While they've mentioned that this is going to be a product that is backwards compatible with the 802.11n-based ePMP 1000/2000 radios, there's no way that this radio will be compatible with the PMP450 line of radios. The two are completely different technologies/product lines.
Secondly, in order for one to get to the 500mbps mark, it requires very large channel widths (80MHz+) which in turn requires a large amount of clean spectrum to work properly. Historically, Cambium has optimized their products for interference mitigation and using smaller channel widths that have a higher chance of success with operators around the globe.
2. "I would like to build my new network with 4, 450m synced."
So just to reiterate, the PMP450 line (including the 450m) is not based on or compatible with 802.11ac. In addition, the performance gains that can be achieved with the 450m are heavily dependant upon the sector having a large number of SM's spread out evenly throughout the sector. Just having a few SM's OR having a bunch of SM's grouped into one small area of the sector's 90deg beamwidth will not be optimal. You'd be wise to just deploy the PMP450i w/integrated 90deg sector, and when that sector reaches upwards of 100 SM's, and/or a high frame utilization, swap it out with the 450m.
3. "But my bottle neck is the sm side."
I'm not sure I understand this as Cambium makes SM's that are unlocked that can get to around 100mbps net under ideal conditions, and if you need further performance, higher PPS, or want to get more performance out of the soon to be released 30 and 40MHz channel width options, you can buy 450i SM's for 5GHz (and soon to be 3.65) that will support well over 100mbps.
4. "Over the past few months i have lost some customers to a provider using the new telrad lte."
Telrad's eNB and UE's (eNb's or eNodeB, and UE's or 'User Equipment' are the same as AP and SM's in Cambium terms, respectively), are using LTE release 9 on the eNb, and CAT4 on the UE. This means that the UE's are limited to 100mbps on the downlink and 50mbps on the uplink. Assuming that the operator is using a 2x2 eNb (and not a 4x4 config), the same throughput limitations as apply. CAT4 UE's are actually, performancewise, slower then the PMP450 SM's in LOS applications. This is because CAT4 UE's are limited to 64QAM on the downlink, and 16QAM and one chain on the uplink.
That being said, LTE allows for more subcarriers (4 times as many as PMP450), which in turn allow for better performance in near and non-LOS conditions. Could it be that perhaps these clients you've missed are in that situation and are getting better near/non-LOS performance from your Telrad competitor?
ALSO, as far as I know, Telrad doesn't have a 5GHz product... just 3.XGHz (TDD band 43) and 2.5GHz (TDD Band 41), so Cambium gives you more band options at your disposal if you're deploying PMP450.
To sum up this comment... Cambium does have faster SM's that will meet your needs i.e 25+ mbps, and secondly, Telrad isn't any faster then Cambium's PMP450 products in LOS applications.