Hi Rick,
I can't imagine the telerik control being as good an upload module as NeatUpload. With normal file uploads the entire file must be in server memory during the upload and with NeatUpload it can stream directly to disk. NeatUpload is an HttpModule that is involved with all requests even if you use some other upload control.
The max file size allowed to upload is determined by Web.config settings subject to enforcement also at the machine.config level.
In the case where NeatUpload is disabled like for Medium Trust by commenting it out in Web.config then the max file upload would be determined by a setting you can put in <system.web> section, by default 4MB is the limit unless you specify it.
<!--
this sets the max size of an upload if the
UploadHttpModule is not being used (ie commented out because it can't work in mediumtrust). In that case, the
entire request is stored in memory so large uploads
could be used as a Denial of Service attack.
use you own judgement in determining the max size of
a request you want to allow.
<httpRuntime maxRequestLength="2097151" executionTimeout="360" useFullyQualifiedRedirectUrl="true" />
-->
When NeatUpload is enabled, then it is determined by the NeatUpload section:
<neatUpload xmlns="http://www.brettle.com/neatupload/config/2008"
useHttpModule="true"
maxNormalRequestLength="4096"
maxRequestLength="2097151"
multiRequestUploadHandlerUrl="~/NeatUpload/MultiRequestUploadHandler.ashx"
maxUploadRate="300"
>
</neatUpload>
I believe that 2097151 is the max possible.
Hope it helps,
Joe