Reliability or Robustness Testing a Web Server - asp.net

Question

I have just built a proof of concept for an asp.net MVC controller to (1) generate a barcode from user input using barcode rendering framework and (2) embed it in a PDF document using wkhtmltopdf.exe
Before telling my client it's a working solution, I want to know it's not going to bring down their website. My main concern is long-term reliability -- whether for instance creating and disposing the unmanaged system process for wkhtmltopdf.exe might leak something. (Peak performance and load is not expected to be such an issue - only a few requests per minute at peak).
So, I run a couple of tests from the Windows command line:
(1) 1,000 Requests in Sequence (ie 1 at a time)
for /l %i in (1,1,1000) do curl ^
"http://localhost:8003/Home/Test?text=Iteration_%i___012345&scale=2&height=50" -o output.pdf
(2) Up to 40 requests sent within 2 seconds
for /l %i in (1,1,40) do start "Curl %i" curl ^
"http://localhost:8003/Home/Test?text=Iteration_%i___012345&scale=2&height=50" -o output%i.pdf
And I record some performance counters in perfmon before, during & after. Specifically I look at total processes, threads, handles, memory, disk use on the machine and on the IIS process specifically.
So, my questions:
1) What would you consider acceptable evidence that the the solution looks to be at low risk of bringing down the server? Would you amend what I've done, or would you do something completely different?
2) Given my concern is reliability, I think that the 'Before' vs 'After' figures are the ones I most care about. Agree or not?
3) Looking at the Before vs After figures, the only concern I see is the 'Processes Total Handle Count'. I conclude that launching wkhtmltopdf.exe nearly a thousand times has probably not leaked anything or destabilised the machine. But I might be wrong and should run the same tests for hours or days to reduce the level of doubt. Agree or not?
(The risk level: A couple of people's jobs might be on the line if it went pear-shaped. Revenue on the site is £1,000s per hour).
My perfmon results were as follows.
700 Requests in Sequence
1-5 Mins 10 Mins
Counter Before Test Min Ave Max After Test
System
System Processes 95 97 100 101 95
System Threads 1220 1245 1264 1281 1238
Memory Available MB 4888 4840 4850 4868 4837
Memory % Committed 23 24 24 24 24
Processes Total Handle Cou 33255 34147 34489 34775 34029
Processor % Processor Time 4 to 30 40 57 78 1 to 30
Physical Disk % Disk Time 1 0 7 75 0 to 30
IIS Express
% Processor Time 0 0 2 6 0
Handle Count 610 595 640 690 614
Thread Count 34 35 35 35 35
Working Set 138 139 139 139 139
IO Data KB/sec 0 453 491 691 0
20 Requests sent within 2 seconds followed by 40 Requests sent within 3 seconds
1-5 Mins 10 Mins
Counter Before Test Min Ave Max After Test
System
System Processes 95 98 137 257 96
System Threads 1238 1251 1425 1913 1240
Memory Available MB 4837 4309 4694 4818 4811
Memory % Committed 24 24 25 29 24
Processes Total Handle Cou 34029 34953 38539 52140 34800
Processor % Processor Time 1 to 30 1 48 100 1 to 10
Physical Disk % Disk Time 0 to 30 0 7 136 0 to 10
IIS Express
% Processor Time 0 0 1 29 0
Handle Count 610 664 818 936 834
Thread Count 34 37 50 68 37
Working Set 138 139 142 157 141
IO Data KB/sec 0 0 186 2559 0